Re: compression on 90 mariner
If it has been quite a while since the carbs were last cleaned, it may be time again. As the idle fuel passages get dirty and flow is reduced you start having idle problems, Clean and replace all gaskets to restore proper fuel flow.
Remember, if the idle circuit is dirty, so is the main, and running with a restricted main will fry a piston. It's just a matter of time, do it now and save a lot of time by not having to rebuild a fried motor later.